Include common system header files in coap_internal.h based on HAVE_*H
definitions.
Remove these system header files from include/*/*.h.
Add in system header files where appropriate in various apps.
Some of the Zephyr include files need to be C++, not C based. The 'extern "C"'
wrapper in include/coap3/coap.h means that all #include are treated as being C.
Remove 'extern "C"' wrapper from include/coap3/coap.h and add wrapper to
include files after #include and before any function / structure definitions.
Add in a C++ build test for CI.
encode.h and str.h are not used in any open PRs and can safely be renamed
with a coap_ prefix.
Order the include lists alphabetically as if all the entries have a coap_
prefix, so when the include file gets renamed with a coap_ prefix, the
include order is not disturbed.
Rename (as these are all internal files) for clarity
coap_mutex.h to coap_mutex_internal.h
coap_hashkey.h to coap_hashkey_internal.h
uthash.h to coap_uthash_internal.h
utlist.h to coap_utlist_internal.h
Jon Shallow